Mechanism of salt migration in icicles during phase transition and its impact on ice flashover

Abstract

This paper addresses the salt migration during phase transition of cooling water in the icicle growth period. This paper contains three parts, first, application of Fick's law in salt migration process; second, salt concentration measurement of icicles in artificial climate chamber; third, ice flashover experiments during melting period. Based on freezing model analysis, cooling water started to freeze from the water-insulator interface. Fick's diffusion law was applied to deduce the change of salt content in the liquid water. It was investigated that the melting water conductivity of icicle tips was proportional to the applied water conductivity. Freezing velocity (in mm/h) played important roles on the salt migration process during the growth of icicles and the melting water conductivity of an icicle tip under 2.6 mm/h was 1.66 times higher than under 3.6 mm/h. Special attention was paid to the ice flashover under non-bridged and bridged icicles. Icing experiments under energized condition showed that the conductivity of icicle tips increased by 70 percent when icicles grew to bridge the gap between adjacent sheds, which was a critical reason for the decline of the corresponding ice flashover voltage.